As mobile devices have been increasingly developed, and the demand for such mobile devices has increased, the demand for secondary batteries has also sharply increased. Among such secondary batteries is a lithium secondary battery exhibiting high energy density and operating voltage and excellent preservation and service-life characteristics, which has been widely used as an energy source for various electronic products as well as for the mobile devices.
However, various combustible materials are contained in the lithium secondary battery. As a result, there is a possibility of danger in that the lithium secondary battery will be heated or explode due to overcharge, overcurrent or any other external physical impacts. In other words, the lithium secondary battery has low safety. Consequently, a protection circuit module (PCM) to effectively control an abnormal state of the lithium secondary battery, such as overcharge, is mounted in the lithium secondary battery in a state in which the PCM is connected to a battery cell of the lithium secondary battery.
Generally, it is necessary for safety elements, including the PCM, to be maintained in electrical connection with electrode terminals of a battery cell and, at the same time, to be electrically isolated from other parts of the battery cell. Consequently, an insulative mounting member is necessary to achieve such connection, and an adhesive agent is applied between the battery cell and the insulative mounting member to achieve the coupling between the battery cell and the insulative mounting member. However, this coupling method may reduce the coupling strength of a battery pack. An electric short circuit may occur in the battery cell due to reduction of the coupling strength, when external impact is applied to the battery cell, with the result that the battery cell may catch fire or explode. In other words, safety-related problems may occur.
Also, an insulative cap is coupled to the top of the battery cell so that the insulative cap surrounds the insulative mounting member in a state in which the safety elements are mounted to the insulative mounting member to protect the battery cell against external impact, to increase the mechanical strength of the members mounted to the top of the battery cell and to maintain electrical insulation of the battery cell.
In this case, the coupling between the insulative cap and the top of the battery cell is generally achieved by bonding. However, this coupling method may also reduce the coupling strength between the battery cell and the insulative cap like the coupling between the battery cell and the insulative mounting member as described above.
Consequently, there is a high necessity for technology to secure stable coupling strength between the battery cell and the insulative cap.